The largest wildfire in Los Angeles County history was 87 percent contained today and air quality in many areas has returned to “acceptable levels,” but the projected time for full containment was moved back four days, authorities said.

Officials had hoped to declare 100 percent containment of the blaze on Tuesday but now say the target date is Saturday. They said the revision results from weather-related delays in carrying out controlled burn operations designed to rob the fire of fuel by safely destroying vegetation.

Crews were reduced by nearly half over the weekend, with about 1,192 firefighters remaining on the line.

Early this afternoon, the South Coast Air Quality Management District reported that the air quality has “returned to acceptable levels, except in the immediate vicinity of the Station Fire in the San Gabriel Mountains.”

“In any area of visible smoke or where there is an odor of smoke, all individuals are urged to be cautious, and to avoid unnecessary outdoor activities,” said Dr. Jonathan Fielding, the county’s director of public health.

Since the arson fire broke out near a Forest Service ranger station in the Angeles National Forest Aug. 26, it has scorched 160,557 acres, making it the largest fire in Los Angeles County history and 10th-largest fire in California since 1933.

The blaze destroyed 89 residences, and 120 others remain threatened, according to the U.S. Forest Service, the lead agency in fighting the blaze. Additionally, 26 commercial properties and 94 outbuildings were destroyed by the fire. The estimated cost of the firefighting effort was $92.6 million.

The fire also claimed the lives of two firefighters whose truck plunged off a mountain road. A public memorial was held at Dodger Stadium Saturday for the two victims. Vice President Joe Biden and Gov. Arnold Schwarzenegger joined thousands of firefighters in honoring Capt. Tedmund “Ted” Hall, 47, of San Bernardino County, and firefighter Specialist Arnaldo “Arnie” Quinones, 35, of Palmdale.